Not to split hairs, but you should switch that around. You can't measure horsepower it has to be calculated from torque and RPM.
I should say thank you for the time you put in to post this. I knew the stocker wasn't very good, but i didn't know how to calculate a new one.
Much appreciated.

 

i don't think it matters that much...they're functions of eachother.

but did mazda calculate peak torque @ 6500 rpm?? nope.

 

Would the calculated length from the formula be equally valid at 10psi guage pressure compared to 0psi (NA)? I'm not sure if the boost pressure would change the speed of sound in the runners.

Also, runner length for the formula is measured from where the port opening starts to the entrance to the manifold plenum after the throttle body?

Thanks rotarygod for a very useful thread. I'm contemplating making an intake manifold with reinforced rubber hoses as runners so I can trim them, but my 6 port street port has different timings for each port so I want to get a ratio of runner lengths set up before I start trimming.

 

I guess he could think that if you were driving anything but a rotary vehicle.

 

Back from the dead again.
How does the formula deal with intakes that "Y" togather such as used for 2BBL carbs? I'm thinking of designing a manifold for my 6-port that uses some 46mm throttlebodies I found, this would require a "Y" and I'm not sure how I'd work that out. I'm also interested in making individual runners for each of the ports so they Aux. ports and the secondaries wouldn't have to share a runner; they would join the primary runners seperately.
Grant

 

THREAD NECROMANCERY GO!

No. Temp changes the speed of sound, not pressure. Getting your runer lengths tuned for your rpm band is still a good idea of course, regardless of your induction system, but pressure doesnt effect it as much as temperature - and even un intercooled air from a turbo aint nearly as hot as exhaust gas.

And yeah, I just totally resurrected this thread because there are still a LOT of people who didnt get the point a few years ago.

 

for intake runner length, are we talking length of intake manifold from flange to flange or are we measuring all the way up thru throttle body to the top of the velocity stack (if you have a stack)?

 

Thanx Rotarygod good read...


Jay7..

 

Sorry to bring this thread back from the dead (again).

I've read as much as i can but at the start you said you would include the calcs for the plenum diameter and length for these equations. Also im confused about the intake diameter, what would be a standard diameter used ?

Im looking at fitting a 13b egi into my 1st gen and its not running on petrol. My current 12a runs on LPG (propane) and i don't have a petrol system in the car.

Im looking at building an intake to have the peek power at about 6k with the engine having a mild or large street port N/A

Cheers

Shaun

 

I'm trying to figure it out for my RB Jport, but with the port opening is rather different, it opens at 115° BTDC and closes at 72° ABDC now my dilema is that I am unsure weather to add or subtract this number.
Where it says "We use 720* as our base point to start figuring out EPD. Since the port opens after TDC, we subtract 32* from 720* to get 688*. Since the port closes 40* after BDC, add 40* to 688* to get a total EPD of 728*." I'm unsure weather I should add 115 because it opens BTDC? Any ideas on this?
Cheers

 

Anyone? Sorry for digging up and old post

 

tons of good info here

 

I think it's about rite

 

ok, i'm looking for a broad powerband. say in IO is 15* ATDC and IC is 60*ABDC

if i tune the primarys to 6000 and secondaries to 7000. i get 16.5 for primary length and 14.06 for secondary length.

and i getting the math right?

 

Please stop referring to this thread. It is outdated and the info needs some serious updating and clarification. Some things are good. Others aren't. There was one fundamental mistake made when I typed this originally but I haven't had time to go rewrite it.

 

good stuff

 

Hi, RotaryGod you say this thread is out of date, is there somewhere you can give a link to where you have addressed the information that you think is incorrect.

Also does anyone know if it's possible to measure port timing on an assembled engine, or is it something that must be done during engine assembly?

One final thing, does anyone know roughly the length of the intake runner in the Irons/side plates, so that the manifold can be calculated and manufactured without having to dissasemble the engine to measure the port runner in the irons.

Cheers, J

 

Hello everyone,

I am currently diving into this for an n/a semi p.p.

I did calculations according to formula's from the first post but now I'm reading that they are not fully correct / out dated.

Anyone that can help out?

 

Sadly, probably not...